I first met my boyfriend when we were in grade 7. Moving on to highschool, I eventually developed feelings for him, and him for me, and we began dating in grade 9/10. Our relationship was pretty good, we had the same interests and spent a lot of time together and I believe I genuinely loved him, and he loved me. It was a great relationship.
Fast forward to the beginning of university. During highschool, we both considered our sexualities, and now we both identify as bisexual. Just before school begins, my boyfriend comes out to me as male-to-female (MtF) transgendered. My boyfriend has essentially become my girlfriend.
[I'll refer to him as 'her' now]
Initially I had no problem with this. I love her dearly and I want her to make a healthy transition to who she truly is, after living a lie for most of highschool. I really believe this is the best thing for her and she's already so much happier and brighter than she has been in about a year.
But as these past 6 months have gone by, I realized I'm not happy. I'm starting to question if I'm in love with her or if I was even in love with her before she came out. I'm scared to break up because I might realize it was all a big mistake and that I really do love her but at the same time I just can't see myself spending the rest of my life with her, and that makes me very sad, because we used to have such a great relationship. Just... recently her quirks I found endearing are become tiresome, and I often feel like spending time together is a chore I need to get over with and look forward to it being over. Also, I feel like she's constantly pressuring me to have sex when I often feel like I don't want to. When I tell her I'm not interested, she gets sulky and the night often ends on a sour note. It's very frustrating.

I want to do my best and the most I can to support her in this difficult time, but I don't know if I can continue to be there romantically for her. At the same time I don't want the huge stress of breaking up to her already extremely stressful life, as she's coming out to many people and starting school as a girl this semester. I want to help her but I'm starting to grow wearing of our 'romantic' relationship.

So maybe you can help me? Am I more upset by this transition than I let myself think at the beginning? Or was I never really invested in this relationship to begin with? It's really hard to identify right now. Thanks for your time.